Bulgarians consider corruption to be their society's most serious problem, an independent democracy watchdog said in a report Monday, AFP reports.The Centre for the Study of Democracy (CSD) said that instances of corruption fell from 150,000 in July 2006 to 115,000 in January 2007, when Bulgaria joined the European Union.But despite this positive development, "grand political corruption involving members of the government, MPs, senior state officials remains a serious challenge", the report said."There is a growing body of public opinion that political corruption is on the rise, almost institutionalized in the corrupt networks that came to be known as 'loops of companies'", chanelling state money towards certain businesses, the report said."Bulgarians for the first time in a decade identify corruption as currently the gravest problem in society," it added.